Abner Kneeland was raised in the Christian faith, and became a Baptist lay minister in 1801, but upon further reflection, reading, and interaction with Universalists he converted to that church in 1803. Ordained the following year, he worked as an itinerant preacher in New Hampshire, and in 1811 he was assigned to a new church in Charlestown, Massachusetts. After three years of service at this pulpit, his faith faltered and he quit the ministry and opened a dry goods store with his wife. He returned to the church in 1816, and returned to the ministry in 1818. Though he had only one year of formal education, he taught himself Latin, Greek and Hebrew, and published his own translation of the New Testament. He also wrote a book that proposed the elimination of silent letters and other improvements to the English language.

By the early 1820s Kneeland had been drawn to the teachings of the utopian communitarian Robert Owen and the political philosophy of William Lloyd Garrison. By the end of that decade his beliefs and teachings had moved so far from the Universalists that he was asked to again resign his ministry and "disfellowshipped" from the church. His radicalization continued, and over subsequent years he called for freedom for slaves, legally equal rights for women and blacks, and legalization of birth control, divorce, and miscegenation (interracial marriage).

It was his perspective on religion, however, that cast Kneeland as one of his era's most controversial people. He was indicted after publication of the 1833 edition of his freethought newspaper Boston Investigator, in which he wrote, "Universalists believe in a god which I do not" and "Universalists believe in Christ, which I do not: but believe that the whole story concerning him is as much a fable and fiction, as that of the god Prometheus...". Prosecuted under a 1782 Massachusetts law that banned "denying, cursing, or contumeliously reproaching God", he argued in court that the law violated the First Amendment, but the judge told the jury that the law was proper and warned of the societal dangers of unpunished blasphemy. Kneeland was convicted, then appealed and was convicted again, and finally he was convicted a third time before the Massachusetts Supreme Court in 1838, and sentenced to sixty days in prison.

The prison sentence was at least as controversial as Kneeland's writings, with numerous editorials nationwide criticizing the Massachusetts law and verdict, and Ralph Waldo Emerson and Oliver Wendell Holmes were among those who spoke of the injustice of the conviction. The Massachusetts law under which Kneeland was convicted remains on the books, and there were several subsequent prosecutions under similar laws in other states, but he is believed to have been the last person jailed for blasphemy in America. After serving his sentence Kneeland moved to Ohio, where he established Salubria, a community near modern-day Farmington, Iowa, intended as a place where freedom of inquiry could be encouraged. He died there six years later, and the community faded shortly thereafter.

Author of books:The Columbian Miscellany (1804)The Child's Spelling Book Containing Easy Words from One to Four Syllables (1808)The American Definition Spelling Book (1814)A Series of Letters, in Defence of Divine Revelation (1816, with Hosea Ballou)A Series of Lectures on the Doctrine of Universal Benevolence (1818)The Philadelphia Hymn Book, or, A Selection of Sacred Poetry consisting of Psalms and Hymns (1819)A Greek and English Testament with Notes (1822)The Deist (1822)Lectures on Universal Benevolence (1824)Lectures of the Doctrine of Universal Salvation (1824, collected sermons)Key to the new System of Orthography (1827)A Review of the Evidences of Christianity (1829)Philosophical Creed (1833)